Chemicals used to kill plants can be classified as either non-selective herbicides or selective herbicides. Non-selective herbicides kill all plants to which they are applied. An example of a non-selective herbicide is N-(phosphonomethyl) glycine, known commonly as glyphosphate or "Roundup.RTM.." A selective herbicide kills only certain plants, that is, it is more toxic to some plants than to others. To be of practical use, a selective herbicide must have the ability to kill undesirable plants without affecting the remaining desirable plants. An example of such a chemical is the well known herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) which will selectively kill broad-leaved weeds in, for example, turf grass. However, there are many weeds which are not destroyed by 2,4-D. Furthermore, 2,4-D is toxic and can cause eye irritation and gastrointestinal disturbances if ingested. Some undesirable grasses, like crabgrass or bermudagrass, can be selectively removed from turf by the use of arsenic compounds, but these herbicides can be toxic to both humans and animals. Other turf weeds, such as nimblewill, are not affected by 2,4-D or arsenic compounds and can only be controlled chemically by using glyphosphate which kills not only the nimblewill but all of the desirable plants surrounding the nimblewill.
U.S. Pat. No. 5,668,086, herein incorporated by reference, discloses the use of a herbicidal composition containing diquat (1,1'-ethylene-2,2'-bipyridinium dibromide) or paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride) as contact herbicides. Diquat and paraquat have no selectivity but exhibit strong week-killing power by foliage treatment. In use, they are diluted with water. An ionic surfactant is further added so that the liquid can be applied evenly and ensure contact with the stems and leaves of the vegetation long enough to penetrate into the plant body. Unfortunately, the addition of the surfactant lowers the herbicidal effects of the composition. The reduction observed in the herbicidal effects observed in the composition is dependent upon the kind and amount of anionic surfactant used.
It is the primary object of this invention to provide a method for the selective control of certain undesirable vegetation using herbicides which are non-toxic to humans, animals and insects. It is a further object to provide such herbicides that also are odorless, water soluble and biodegradable.